POM vs PA66: Mechanical Properties, Cost & Application Comparison

Where POM Excels

Dimensional Stability in Humid Environments

POM‘s most significant advantage over PA66 is its dramatically lower moisture absorption. At saturation, PA66 absorbs up to 8% water by weight, causing:

· Dimensional swelling of 2–3%

· Reduction in tensile strength of 30–50%

· Decrease in flexural modulus of 50–70%

POM absorbs only 0.8% at saturation, maintaining dimensional tolerances and mechanical properties even in high-humidity or submerged applications.

Fatigue Resistance

POM‘s high crystallinity (75–85%) gives it outstanding fatigue resistance — the ability to withstand millions of loading cycles without failure. This makes POM the preferred material for:

· Gear wheels and racks

· Clip fasteners and snap-fit mechanisms

· Spring components and latches

· Conveyor belt links

Food Contact Compliance

Natural POM (both homopolymer and copolymer) is FDA compliant under 21 CFR §177.2470/2480. PA66 is not FDA approved for food contact due to amine migration concerns. This makes POM the automatic choice for food processing equipment.

Chemical Resistance

POM resists organic solvents, fuels, oils, and weak acids/bases better than PA66. PA66 is attacked by strong acids, bases, and some polar solvents that POM tolerates.

Where PA66 Excels

Higher Impact Strength

PA66‘s superior impact toughness (50% higher than POM) makes it the preferred choice for components subject to sudden impact loads — bumper brackets, tool housings, and protective covers.

Higher Temperature Resistance

PA66‘s continuous service temperature of 120°C (vs POM‘s 100°C) and higher HDT gives it an edge in under-hood automotive and industrial heating applications.

Cost Advantage

PA66 is typically 20–40% cheaper than POM, making it attractive for high-volume applications where POM‘s advantages (dimensional stability, wear resistance) are not critical.

Reinforcement Response

PA66 responds better to glass fibre reinforcement. PA66 GF30 achieves tensile strengths of 180 MPa, while POM GF30 reaches only 140 MPa. This makes glass-filled PA66 the preferred structural plastic for automotive and industrial components.